<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>下拉菜单案例</title>
    <style>
        *{
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            list-style: none;
        }

        body{
            margin: 0;
            width: 100vw;
            height: 100vh;
            background-color: linear-gradient(to right,#f8b2cf,#a2eaea);

        }
        
        .box{
            display: flex;
            position: fixed;
            top: 50%;
            left: 50%;
            transform: translate(-50%,-50%);
        }

        .nav{
            width: 1000px;
            height: 65px;
            background-color: #6bcab0;
            display: flex;
        }

        .nav a{
            display: flex;
            justify-content: center;
            align-items: center;
            height: 100%;
            color: #fff;
            font-size: 18px;
        }

        .nav .item{
            width: 20%;
            height: 100%;
            position: relative;
        }

        .list{
            position: absolute;
            top: 65px;
            width: 100%;
            overflow: hidden;
            max-height: 0;
            transition: all ease 0.4s;
            border-radius: 0 0 10px 10px;
            background-color: #ea7592;
        }

        .itemTwo{
            height: 65px;
            transition: all ease 0.4s;

        }

        .nav .item:hover{
            background-color: #ea7592;
        }


        .nav .item:hover .list{
            max-height: 500px;
        }

        a{
            text-decoration: none;
        }
        
        .itemTwo:hover{
            background-color: rgba(255, 255, 255, 0.3);
        }

    </style>

</head>
<body>
    <div class="box">
        <ul class="nav">
            <li class="item">
                <a href="#">人工智能技术</a>
                <ul class="list">
                    <li class="itemTwo"><a href="#">Python</a></li>
                    <li class="itemTwo"><a href="#">LISP</a></li>
                </ul>
            </li>
            <li class="item">
                <a href="#">前端技术</a>
                <ul class="list">
                    <li class="itemTwo"><a href="#">HTML</a></li>
                    <li class="itemTwo"><a href="#">CSS</a></li>
                    <li class="itemTwo"><a href="#">JavaScript</a></li>
                </ul>
            </li>
            <li class="item">
                <a href="#">数据库技术</a>
                <ul class="list">
                    <li class="itemTwo"><a href="#">SqlServer</a></li>
                    <li class="itemTwo"><a href="#">MySQL</a></li>
                </ul>
            </li>
            <li class="item">
                <a href="#">后端技术</a>
                <ul class="list">
                    <li class="itemTwo"><a href="#">Java</a></li>
                    <li class="itemTwo"><a href="#">C++</a></li>
                    <li class="itemTwo"><a href="#">C#</a></li>
                </ul>
            </li>
            <li class="item">
                <a href="#">开发框架</a>
                <ul class="list">
                    <li class="itemTwo"><a href="#">Vue</a></li>
                    <li class="itemTwo"><a href="#">React</a></li>
                    <li class="itemTwo"><a href="#">SpringBoot</a></li>
                </ul>
            </li>

        </ul>
    </div>
</body>
</html>